A filtration system having a filter medium belt is typically used to filter metalworking fluids, such as machining coolants, to remove chips and grit so that the fluids can be reused. In such a filtration system, the filter medium belt, disposed in a tank, is moved over a perforated plate support. The fluid to be filtered passes through the filter medium and the perforated plate support under gravity and/or under a pressure generated by a vacuum below the perforated support plate. The filter medium belt is periodically indexed to bring a fresh segment atop the perforated support plate to replace a dirty segment.
The filter medium can be a reusable filter medium, such as a circular, endless filter medium belt, which is indexed periodically as the filter medium becomes dirty, and the dirty segment is then cleaned and reused. Alternatively, the filter medium can be of the disposable type, and the used filter medium is collected for disposal.
The filter medium belt is often driven by a flight conveyor having chain links connected by flights extending across the width of the filter medium belt, which flights may also carry the removed solids out of the tank.
The conveyor can either be attached to the filter medium in the case of a reusable filter medium, or merely frictionally engaged with the filter medium to drive the filter medium often in the case of a disposable filter medium.
A seal is provided to seal each side edge of the filter medium belt to prevent unfiltered fluid from getting under the edge and bypassing the filter medium. One type of seal is in the form of an inflatable tube, which extends along the side edge of the filter medium belt and is inflated with air or liquid during filtering and deflated during indexing to allow the filter medium to move freely without inference from the seal. A second type of seal is a seal that can be lowered during filtering and raised during indexing.
One of the disadvantages associated with these two types of seals is that it is time-consuming to inflate and deflate, or to lower and raise, the seal each time the filter medium is indexed. Another disadvantage is that there is the risk that unfiltered fluid may get under the filter medium edge each time the seal is deflated or raised.
Alternatively, a third type of seal is not deflated or raise when the filter medium is indexed. However, this approach creates wear on the filter medium and seal and may cause distortion or tear of the filter medium.